In oil field operations, reciprocating pumps are used for various purposes. Reciprocating pumps are used for operations such as cementing, acidizing, or fracturing of a subterranean well. These reciprocating pumps run for relatively short periods of time, but they operate on a frequent basis and oftentimes at extremely high pressures. A reciprocating pump is mounted to a truck or a skid for transport to various well sites and must be of appropriate size and weight for road and highway regulations.
Reciprocating pumps or positive displacement pumps for oil field operations deliver a fluid or slurry, which may carry solid particles (for example, a sand proppant), at pressures up to 20,000 psi to the wellbore. A known pump for oilfield operations includes a power end driving more than one plunger reciprocally in a corresponding fluid end or pump chamber. The fluid end may comprise three or five plunger bores arranged transversely across a fluid head, and each plunger bore may be intersected by suction and discharge valve bores. In a known reciprocating pump, the axis of each plunger bore intersects perpendicularly with a common axis of the suction and discharge valve bores.
In a mode of operating a known three plunger bore reciprocating pump at high fluid pressures (for example, around or greater than 20,000 psi), a maximum pressure and thus stress can occur within a given pump chamber as the plunger moves longitudinally in the fluid end towards top dead center (TDC), compressing the fluid therein. One of the other pump chambers will be in discharge and thus at a very low pressure, and the other pump chamber will have started to compress the fluid therein.
It has been discovered that, in a given pump chamber, the areas of highest stress occur at the intersection of each plunger bore with its suction and discharge valve bores as the plunger moves to TDC. The occurrence of high stress at these areas can shorten the life of the fluid end.
JP 2000-170643 is directed to a multiple reciprocating pump having a small size. The pump has three piston bores in which the pistons reciprocate but, so that a compact pump configuration can be provided, the axis of each suction valve bore is arranged perpendicularly to its respective discharge valve bore (that is, so that there is a laterally directed discharge from the fluid end).
JP 2000-170643 also teaches that a limit as to the volume of fluid that can be pumped by a small reciprocating pump is the size of suction and discharge valve bores. Contrary to the embodiments disclosed herein, the teaching of JP 2000-170643 is not concerned with reducing stresses arising at the intersection of piston, suction and discharge bores. Rather, J P 2000-170643 teaches moving the axes of each of the outside suction and discharge valve bores outwardly with respect to their plunger bore axis to enable the volume of each of the suction and discharge valve bores to be increased. Thus, with an increased pump speed, an increased volumetric flow can be achieved with a pump that still has a similar overall dimensional profile. In addition, JP 2000-170643 teaches that the valve bores are moved outwardly without increasing the amount of material between the suction and discharge bores. This is because the reconfiguration of the pump in JP 2000-170643 is not concerned with reducing stresses within the pump in use.